Electronic frequency error detector



April 1966 A. B. BLACKBURN 3,244,937

ELECTRONIC FREQUENCY ERROR DETECTOR Original Filed Sept. 26, 1962 Fig.

S/G/VAL CIRCUIT INVENTOR ALAN BLACKBURN ATTORNEY5 United States Patent3,244,937 ELECTRONIC FREQUENCY ERROR DETECTOR Alan B. Blackburn, Troy,Qhio, assignor to Hobart Brothers Company, Troy, (lliio, a corporationof Ohio Continuation of application Ser. No. 226,209, Sept. 26, 1962.This application Oct. 8, 1965, Ser. No. 493,997' 2 Claims. ((31. 317, 9)

This application is a continuation of Serial No. 226,209, filedSeptember 26, 1962, and now abandoned.

I The present invention relates to an electronic frequency errordetector.

It is the primary object of the present invention to devise a new andimproved frequency error detector which can be used atlernatively asoverand under-frequency detector.

It is an object of the present invention to provide a frequency errordetector with remote control and signalling.

It is another object of the present invention to provide a novel,miniaturized frequency error detector responding to 11% frequencyvariation while using a simple control and/or signalling relay.

It is a further object of the present invention to provide a novelfrequency error detector with an adjustable range of tolerance.

It is still a further object of the present invention to provide a newfrequency error detector which permits installation to a given powerline of any voltage within a wide range without requiring special prioradaptation.

According to one aspect of the present invention in a preferredembodiment thereof, it is suggested to provide an impedance bridge inwhich there are opposite branches of similar and adjacent branches ofdissimilar type; two branches may comprise ohmic resistors and the othertwo branches capacitors, with respectively shunted resistors to reducethe effect of power line harmonics. The main input terminals of thisbridge are connected or connectable to the line, the frequency of whichis to be supervised. The output diagonal of the bridge is interconnectedby a series circuit connection comprising, in succession, a diode, apotentiometer and another diode poled for similar current direction. Thetap or slider of the potentiometer and one main bridge terminal areinterconnected by the base emitter path of a transistor. The transistorcontrols the current through a relay coil, preferably being shuntedacross the emitter-collector path of the transistor. The relay governsthe current supply to a signalling device, for example, a lamp.

The objects and features of the invention will be better understood fromthe following description of the drawing in which:

FIG. 1 illustrates a schematic circuit diagram of a frequency errordetector with signalling device in'accordan'ce with an embodiment of thepresent invention; and

FIG. 2 illustrates a modified device as compared with that illustratedin FIG. 1 for over and under-frequency detection.

In FIG. 1 there is first shown a prime mover 1, for example, an internalcombustion engine or an electric motor, driving a 400 c.p.s.-four wiregenerator 2. There are three phase lines R, S, T, and a neutral line Nconnecting generator 2 to a load.

It should be mentioned that the electric generator and the motor typeare not important; however, the invention finds best utility in case ofa combustion engine. since here it is more likely that frequencydeviations will occur. Of course, the generator has to. be an A.C.generator since the invention is related to frequency error detection,but the phase type of the power line to be supervised is not important.

There are two sensing terminals A and B connected and 3,244,937 PatentedApr. 5, 1966 ice pertaining to lines R and N, respectively, to. whichsensing terminals there is connected the frequency detector to bedescribed below.

Two main circuit breakers, 3. and 4 are provided to make. and breakcontact in the feeder lines N, R, S, T leading to the load.

It can be seen from the drawing that terminal B is not governed by anyof the contacts of circuit breakers 3 and 4 so that the. detectorcircuit to be described below is. always. connected to line N whichpreferably is connected to ground.

Sensing terminal A is governed by a contact blade of circuit breaker-3., but not by circuit breaker 4. The energizing coil of circuit breaker3 is connected to line N behind its associated contact for this line,while the energizing coil of circuit breaker 4. is connected ahead ofits contact thus governing the connection of line N to the load. Bothcircuit breakers are connected to line R at the generator. There is anormally open starter switch 5 for connecting temporarily the coil ofcircuit breaker 3 to line N at the generator. There is a normally closedoff switch 6 in the return in the return line of the coil of circuitbreaker 3 to line R.

Both the circuit breakers 3 and 4 have individual control circuits governed. by the detector circuit connected across terminals A and B. Tothese terminals A and B is connected a phase-bridge 11 having two ohmicresistance branches 1 2 and 13 and two predominantly capacitive brancheswith capacitors 14 and 16 and parallel resistors, 15 and 17,respectively. The voltages taken from diagonal terminals 18 and 19 arealternating voltages, taken, for example, with respect to terminal B. Arectifier diode 20 is connected to terminal 18, and a rectifier diode 21is connected to terminal 19. These diodes, rectify. the respectivevoltages at these diagonal terminals; thus, at the respective diodeelectrodes not connected to any bridge terminal, pulsating D.C. voltagesappear, which voltage pulses are successively of opposite polarity.

The diodes are interconnected by a potentiometer 22 having an adjustableslider 23. This potentiometer 22 acts as summing member for the twopulsating D.C. voltages, one being taken between and from terminal 18andterminal B, via dioderectifier 20, and the other one is taken fromterminals 19 via diode rectifier 21. The slider 23. is connected; toterminal N by means of a filtering capacitor 24.

If slider 23 is in its centr-al position, the pulsating DC.

,voltage. across. the left hand portion of the potentiometer equals thepulsating DC. voltage across the right hand portion thereof, but, is of;opposite polarity, so the relative potential difference between slider23 and terminal B is zero, provided, that, during operation, theamplitude of the AC. voltage drop across resistor 12 equals theamplitude of the AC. voltage drop across capacitor 16 (ie. the voltageacross capacitor 14 equals that across res istor,13-) Bridge 11 isselected so that at the desired frequency'these operating conditions arepresent indeed. The capacitive connection of slider 23 and terminal Bdoes notalter this mode of operation since the capacitor 24 is effectivein both diode'branches, each one taken between slider 23 and one of thebridge diagonal terminals. It is understood, of course, that thetransistor itself, provides a resistance path paralleling capacitor 24.If slide1123tv is shifted from its central position to the right, the.potential thereof will be negative with respect to that of terminal B;if slider 23 is shifted to the left, there, will be a positive. voltagebetween slider 23 and terminal B From the foregoing, it will beappreciated that bridge 11 was assumed to have similar resistivebranches (l2 and 13) and similar capacitive branches (14, 15 and 16,

17), and that at a given frequency the voltage drop across I allbranches is similar. This similarity is reasonable from the standpointof facilitating the organization of the device and the understanding ofthe invention, but such similarity is not essential. The effectiveimpedance (Z) in ohms of the branch consisting of elements 16 and 17will not be similar to that of the resistance 12 at a deviation from agiven frequency. In view of the fact that slider 23 can be adjusted atwill, one will be able to always find a position of slider 23 in whichits potential is that of terminal B. Of course, with a bridge havingsimilar resistive and similar capacitive branches, there will be nobasic wave (a zero-harmonic) appearing between slider 23 and terminal B,and thus, capacitor 24 has to filter only the ripples caused by higherharmonics, at the adjusted neutral position of slider 23. No fundamentalfrequency will appear at 23 anyway due to the action of rectifiers 20and 21. In case of proper circuit symmetry and sine wave voltage ofproper frequency between A and N, the voltage pulses will cancel atslider 23. However, when the frequency changes the voltages will notcancel but the pulsating voltages will not effect the average collectorcurrent of the transistor; the capacitor 24 charges to very nearly thepeak value of the pulse difference causing a definite D.C. level to beimpressed on the transistor base, which then has an effect on collectorcurrent.

Continuing now with the description of the figure, the voltage betweenslider 23 and terminal B is supplied to the base-emitter path of aNPN-transistor 25, being con nected accordingly, and appearing in commonemitter configuration. A relay coil 26 is connected across emitter andcollector electrodes of transistor 25 and controlled therewith. Acapacitor 27 is connected across relay coil 26 to reduce chattering ofthe relay. A blade 2% is controlled by coil 26. Blade 2% governs thecurrent supply from a suitable voltage source 41 to a signalling lamp2%. The signal-ling and control relay having coil 26 has a second blade29c governing the current supply to circuit breaker 4. The collector oftransistor 25 is connected via a collector resistor 28 and a diode 40 toterminal A, thus being biased with the voltage potential derivedtherefrom. Elements 20 to 29 and 29b constitute a signalling circuitresponding, as will be explained more fully below, to a frequencydeviation below the desired frequency. The contact blade 29c inconjunction with circuit breaker 4 completes this signalling circuit toa control circuit responding in case of an under frequency. The FIGURE 1shows, furthermore, elements 30 to 39 and 39b, respectively,corresponding to elements 20 to 29 and 29b and the former elements areconnected in similar circuit connection as the latter, with the sole,but important, exception for a reversal of the direction of conductionof diodes 30 and 31, as compared with that of diodes 29 and 21. Forreasons of a simplified design, preferably corresponding elements arenot only similar in character and type but also in their dimensions. Thegroup including elements 20 to 29 and 29b serve for detecting andsignalling under-frequency and, as will also be explained below, thegroup comprising elements 30 to 39 and 3% serves to detect and signalover-frequency. Both groups of elements operate independently, but, ofcourse, with mutually exclusive response to a frequency deviation.Over-frequency signalling system 30 to 3% is supplemented by a controlblade 39c likewise controlled by relay coil 36 and governing the currentsupply to circuit breaker 3.

For the operation of the invention it is necessary only that at leastone group of elements as present, since in cases one might be interestedin either under-frequency or over-frequency only.

The device as described thus far operates as follows:

When starter switch is open, the off-switch 6 was previously opened,circuit breakers 3 and 4 are unenergized which means that theirassociated contacts are open.

Throughout the detector circuit ground potential will prevail.

Setting the device into operation, switch 5 is closed thus causingcircuit breaker 3 to respond since unenergized relay 36 keeps blade 29cnormally closed. It might be advisable to have blades inserted into theenergizing circuits of relay-s 26 and 36 so that during the startingoperation, the detector circuit is given time to establish stationaryoperating conditions, so as to prevent any of the relays 26 and 36 fromresponding before transistors 25 and 35 are rendered conductive.

After response of circuit breaker 3, circuit breaker 4 likewise respondsand upon release of switch 5 the two circuit breakers remain energizedkeeping their contacts closed.

If the voltage at terminals A and B has the correct frequency, the DC.voltages derived from bridge 11 by rectifiers 20 and 30 equal thevoltages derived from the bridge by rectifiers 21 and 31. The sliders 23and 33 are adjusted so that they have a slightly positive DC. potentialas compared with that of terminal B. Capacitors 24 and 34 remove thepulsations and ripples of this potential. The positive potentials of thesliders respectively base bias transistors 25 and 35 to conduction, andthe remaining current through the two coils 26 and 36 is insuflicient toenergize the respective relays. Accordingly, blades 2% and 3912 are openand lamps 29a and 39a are dark, indicating that there is correctfrequency in the lines of the terminals A and N. Blades 23c and 39c areclosed causing the circuit breakers to keep their contacts closed.

If the frequency of the voltage at terminals A and B now decreases, thevoltages across capacitors 14 and 16 increases, and the voltages acrossresistors 12 and 13 will decreae thus altering the balance of the bridgeand decreasing the voltage potential of slider 23. Dependent upon prioradjustment of slider 23, at a thus given frequency deviation, thepotential at slider 23 will cause transister 25 to be shifted tocut-off, thus acting as extremely high impedance and permittingincreased current conduction through coil 26. Hence, this signalling andcontrol relay will respond and close its blades 29b so that signallinglamp 29a can light up. Upon response of this relay, blade 290 is opened,interrupting the energizing circuit for circuit breaker 4 which opensits contacts. This circuit breaking is neither effective for circuitbreaker 3 nor for the detector circuit, particularly the potentials atthe sensing terminals A and B thereof. Thus, the sensing of the outputfrequency of generator 2 continue-s.

With regard to transistor 35 its positive base bias was increased withdecreasing frequency, thus increasing the colleictor current, and relaycoil 36 will not become energize When the frequency increases again, thebias of the base electrode of transistor 25 is shifted towards morepositive values until resistor 25 is rendered conductive again and therelay with coil 26 is deenergized so that lamp 29a is turned off again.

Simultaneously, blade 29c closes the energizing circuit for circuitbreaker 4, its contacts close and normal operatron is resumed. This iscarried out fully automatic. Upon a further frequency increase,transistor 25 remains conductive and coil 26 remains deenergized so thatlamp 29a remains dark.

The frequency increase now under consideration causes the voltagesacross resistors 12 and 13 to increase andthe voltages across capacitors14 and 16 to decrease. Accordingly, the voltage potential of slider 33is shifted towards negative values, and, dependent upon the particularadjustment of slider 33, transistor 35 will be cut off at a givenfrequency deviation, so that relay coil 36 will be energized andsignalling lamp 39a is lit up thus indicating the occurrence of anover-frequency at terminals A and B. Simultaneously, blade 39c opens,interruptingthe energizing circuit circuit breaker 3 so that itscgntacts open. This has the effect oftaking the potential at.A away fromthe detector, and the contact blade of circuit breaker 3 governing lineN operates to retain the unenergized condition;for. circuit breaker 3regardlesspf th e positionof blade 39c. Thus, in this instance; therewill be no automatic resuming. of normal operation, but starter switch 5has to be pushedagain. The fact that circuit breaker 4.;droppedsimultaneously with circuit breaker 3 serves as additionalsafeguard. Thepurpose .of this arrangement is that over-frequency usual- .lyis e ydanger u fqreq nmc im r n is underfrequency. Thus, resuming olfoperationis not possible, even accidentally, -unt il personnel have checked onthe cause of the over-frequency and made the necessary repairs oradjustments etc.

The circuit network as described, illustartes the principle behind thisspecific embodiment of the invention. The bridge 11 together with anyofthe diode-potentiometer circuits (20, 21, .22 or .30, 31,. .32) providefor an adjustable D.C. potential at respective potentiometer slider sothat there is an adjustable positive or negative to any one of the mainbridge terminals (or power lines). Such potential depends upon the linefrequency. For any particular frequency within a certain range one canfind an adjustment position of the potentiometer slider (neutral or zeroposition) so that there is no potential difference between this sliderand one of the main bridge terminals (here B).

Upon calibration for a predetermined frequency, such neutralpotentiometer-slider position can be predetermined and define-d as beingassociated to such frequency. Starting out from such a position, onethen can shift the potentiometer slider to another position so thatthere is a particular and predetermined voltage between the slider andthe main bridge terminal under consideration still taken at suchpredetermined and unaltered frequency. This voltage determines the rangeof tolerance. One then has to connect the emitter-base path of atransistor between slider and main terminal so that the transistor iscut off (or conductive). If now the frequency varies so that thisvoltage between slider and main terminal decreases towards zero (theslider remaining in position), the transistor will be renderedconductive (or cut on); no change in conductivity (except in degree) ofthe transistor occurs if the frequency has varied in opposite directionso as to increase the voltage between slider and terminal.

From the foregoing it can be derived that the embodiment shown issusceptible to several specific modifications. Taken in connection withthe bridge 11, the group of elements 20 to 2B or 30 to 38 provides for acontrol circuit in which the respective relay is energized, and theassociated transistor is cut oif in one range of frequency, and in whichthis relay is deenergized with the transistor being conductive in theadjacent frequency range whereby adjustment of the slider (23 or 33) ofthe associated potentiometer shifts the margin or border between the twofrequency ranges. Whether the frequency range in which the respectiverelay is energized (and the transistor is cut off) is the, relativelyspeaking, high frequency range or the low frequency range depends solelyupon the polarity of connecting the diodes (20, 21 or 30, 31) into thecircuit. The relays respectively having coil 26 and 36 can be devised ashaving operating contacts (as is shown) or they may have open-circuit orresting contacts. In this case, lamp 29a when lit up, will actuallyindicate over-frequency, andlamp 39a under-frequency, and theconnections to circuit breakers 3 and 4 will be reversed. With a givenbridge 11, the position of slider 23 or 33 determines the tolerance offrequency deviations from the normal or desired frequency. It is notnecessary to have this range of tolerance for negative deviationssimilar in size to the range of tolerance for .6 positive deviationsfrom normal, i.e. these tolerance ranges are individually adjustable.

Another possible main ains is to have any of the circuit .breakerscontrolling the ig'nitiori circuitif 1 is an internal combustion engine.In this case, the control effect would affect the priiiie mover ratherthan the generator-load circuit.

The capacitors 14. and 16 assassinated reactance coils, and in this.case, the changein voltage with changing frequency is eppqn eiydirected as compared with that of the bridge illustrated ,It is alsopossible to have reactance coils instead or ohmic resistors 12mm 13,provided there is no resonance or anti resoriancin the rangeoffrequencies in which occur the normal frequency and, possible aev'ianensnterermm.

It is further possible to use PNP transistors in which case, as comparedwith the one illustrated, the frequency range causing transistorconduction and the frequency range causing cut oif will be exchanged. Ofcourse, if the mode of operationas far as signalling is concerned isused as described in connection with the drawings, slider 23 then mustbe adjusted to normally bias the base electrode of the then associatedPNP transistor with a positive voltage.

It is furthermore possible to have the elements 20 to- 29 and 2%, 39 and39a connected as illustrated while elements 30 to 38 are connected sothat one side of capacitors 34 and 37 of coil 36 and the emitter oftransistor 33 are connected to terminal A, while the collector resistor38 of transistor 35 is connected to terminal N via an additional diode.

In addition to the signalling lamps illustrated or in lieu thereof, theymay be provided audible signalling means of known design.

FIGURE 2 illustrates a modification and simplification of FIGURE 1,using but one transistor and signalling relay and half the sensingbridge.

In operation, two charging paths are supplied for capacitors 24 and 34,one predominately capacitive through capacitor 14, the otherpredominately resistive through resistor 13. Capacitors 24 and 34 are solarge compared to capacitor 14 that they have little effect on theimpedance of the circuit. This allows alternate positive and negativepulses to charge capacitors 24 and 34 through diodes 20, 21., 30, 31,and potentiometers 22 and 32. It can be seen that, with proper selectionof components, adjustment of potentiometers and correct voltage andfrequency applied, there will be no net charge on capacitors 24 and 34as the impedance of the resistive (chiefly resistor 13) and capacitive(chiefly capacitor 14) branches will be equal.

If the frequency were to be raised, positive pulses on capacitor 24would he larger than the negative and a net positive voltage would beapparent across capacitor 24 (with respect to terminal B). This wouldallow conduction of diode 42, with resultant change in base bias oftransistor 44, causing it .to conduct and reduce the current through thecoil of relay 46, with subsequent closure of its normally closedcontacts to signal a frequency error.

If the frequency were to return to normal, the bias on the base oftransistor 44 would reduce allowing the transistor to cut oif and therelay coil 46 would then have sufficient current through it to attractthe armature and open the normally closed contact to signal correctfrequency.

In the case of reducing the frequency, essentially the same thinghappens only involving potentiometer 3-2, capacitor 34, and diode 43.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departure from thespirit and scope of the invention are intended to the covered by thefollowing claims.

I claim:

1. An electronic frequency error detector for controlling the outputcircuit of an A.C. power supply in response to the frequency of saidpower supply, said error detector comprising a first frequencysensitive, adjustable circuit means operably connected to said powersupply for providing an output signal when the frequency of said powersupply is below a predetermined lower limit, a second frequencysensitive, adjust-able circuit means operably connected to said powersupply for providing an output signal when the frequency of said powersupply is above a predetermined upper limit, a first control circuitmeans in said A.C. power supply circuit opera'ble in response to theoutput of said first frequency sensitive means to open said power supplycircuit when the frequency of said power supply decreases below saidpredetermined lower limit, a second control circuit means in said A.C.power supply circuit operable in response to the output of said secondfrequency sensitive means to open said power supply circuit when thefrequency of said power supply increases above a predetermined upperlimit, and a holding circuit completed through said second controlcircuit means to enable said first and second control circuit meansduring periods when the frequency of said power supply is below saidpredetermined upper limit and to disable said control circuit means andsaid holding circuit when the frequency of said power supply increasesabove said predetermined upper limit thereby preventing an output fromsaid A.C. powersupply after the frequency of said power supply increasesabout said predetermined upper limit until such holding. circuit ismanually restored.

2. The electronic frequency error detector as defined in claim 1 whereinsaid first control circuit means disables the output of said A.C. powersupply only during periods when the frequency of said power supply isbelow said predetermined lower limit and automatically enaibles theoutput of said A.C. power supply when the frequency is above saidpredetermined lower limit.

No references cited.

NEIL C. READ, Primary Examiner.

D. K. MYER. Assistant Examiner.

1. AN ELECTRONIC FREQUENCY ERROR DETECTOR FOR CONTROLLING THE OUTPUTCIRCUIT OF A.C. POWER SUPPLY IN RESPONSE TO THE FREQUENCY OF SAID POWERSUPPLY, SAID ERROR DETECTOR COMPRISING A FIST FREQUENCY SENSITIVE,ADJUSTAABLE CIRCUIT MEANS OPERABLY CONNECTED TO SAID POWER SUPPLY FORPROVIDING AN OUTPUT SIGNAL WHEN THE FREQUENCY OF SAID POWER SUPPLY ISBELOW A PREDETERMINED LOWER LIMIT, A SECOND FREQUENCY SENSITIVE,ADJUSTABLE CIRCUIT MEANS OPERABLY CONNECTED TO SAID POWER SUPPLY FORPROVIDING AN OUTPUT SIGNAL WHEN THE FREQUENCY OF SAID POWER SUPPLY ISABOVE A PREDETERMINED UPPER LIMIT, A FIRST CONTROL CIRCUIT MEANS IN SAIDA.C. POWER SUPPLY CIRCUIT OPERABLE IN RESPONSIVE TO THE OUTPUT OF SAIDFIRST FREQUENCY SENSITIVE MEANS TO OPEN SAID POWER SUPPLY CIRCUIT WHENTHE FREQUENCY OF SAID POWER SUPPLY DECREASES BELOW SAID PREDETERMINEDLOWER LIMIT, A SECOND CONTROL CIRCUIT MEANS IN SAID A.C. POWER SUPPLYCIRCUIT OPERABLE IN RESPONSE TO THE OUTPUT OF SAID SECOND FREQUENCYSENSITIVE MEANS TO OPEN SAID POWER SUPPLY CIRCUIT WHEN THE FREQUENCY OFSAID POWER SUPPLY INCREASES ABOVE A PREDETERMINED UPPER LIMIT, AND AHOLDING CIRCUIT COMPLETED THROUGH SAID SECOND CONTROL CIRCUIT MEANS TOENABLE SAID FIRST AND SECOND CONTROL CIRCUIT MEANS DURING PERIODS WHENTHE FREQUENCY OF SAID POWER SUPPLY IS BELOW SAID PREDETERMINED UPPERLIMIT AND TO DISABLE SAID CONTROL CIRCUIT MEANS AND SAID HOLDING CIRCUITWHEN THE FREQUENCY OF SAID POWER SUPPLY INCREASES ABOVE SAIDPREDETERMINED UPPER LIMIT THEREBY PREVENTING AN OUTPUT FROM SAID A.C.POWER SUPPLY AFTER THE FREQUENCY OF SAID POWER SUPPLY INCREASES ABOUTSAID PREDETERMINED UPPER LIMIT UNTIL SUCH HOLDING CIRCUIT IS MANUALLYRESTORED.